colonoscopy, interpreted the axial images, and used commercially available software to re construct endoluminal perspective views to differentiate polyps from folds. SUBJECTS AND METHODS. We prospectively examined44 patients(27 men and 17women; mean age, 58 years old) with CT colonography by interpreting the axial images and us ing three-dimensional rendering for problem solving only. The CT scans were interpreted by two radiologists who were unawareof patients' histories as revealedby colonoscopic fIndings. The findings on colonography were compared with thoseof conventional colonoscopy to determine sensitivity, specificity, time spent on interpretation, and confidence of interpretation. RESULTS. Colonoscopyshowednormal findingsin 28 patientsand 22 polypsin the re maining 16 patients. Six polyps were 8 mm or larger, three were 5â€"7mm, and 13 were 5 mm or smaller. The findings of the two observers revealed an overall sensitivity of 50% and 38%, respectively, and a specificity of 93% and 86%, respectively. Sensitivity for polyps larger than 8 mm was 83% and specificity was 100% for both observers. The average amount of time spent on interpretation was 28 mm 30 sec (range, 14â€"65 mm). Both observers used the en doluminal view for differentiating folds from polyps in 23 (52%) of 44 patients, which had only minimal impact on interpretation time. CONCLUSION.CT colonographycan be performedand the imagesinterpretedusing currentlyavailablehardwareandsoftwareby initially usingtheaxial imagesto searchfor pol yps of significant size. Endoluminal views should be used only when necessary to help distin guish normal folds from fixed raised lesions that are suggestive of polyps. C olonography (also called virtual oolonoscopy)isaninteractive method of showing cross-sectional volumet nc data of the colon from an endoluminal per spective [1â€"10]. For colonography to be a clinically practical means of evaluating the cleansed colon for polyps and masses, it must be feasible to obtain, display, and interpretthe images in a cost-effective and time-effective fashion using readily available hardware and software. Ham et al. [6] usedproprietary soft ware to display both axial and multiplanar re constructedviews of CF colonography scans, including views parallel to the colonic axis and front and rear endoluminal perspective views.They reported70 consecutive cases, excluding hyperplastic polyps from their analysis, and concluded thatCF colonography wassuperior to axial views alone for detecting polyps 10 mm or larger and that the sensitivity and speci ficity of CF colonography were 75% and 90%, respectively, versus 58% and74% for axialim ages alone [6]. The aim of our study was to evaluate CF colonographyby initially interpreting the axial imagesand then using commercially available (rather than proprietary) software to reconstruct endoluminal perspective views as a limited problem-solving procedure to differentiate pol yps from folds. We prospectively examined 44 patients who underwent CF colonography with three-dimensional(3D) probl...

Detector characterization with modulation transfer function (MTF) and detective quantum efficiency (DQE) inadequately predicts image quality when the imaging system includes focal spot unsharpness and patient scatter. The concepts of MTF, noise power spectrum, noise equivalent quanta and DQE were referenced to the object plane and generalized to include the effect of geometric unsharpness due to the finite size of the focal spot and the effect of the spatial distribution and magnitude of x-ray scatter due to the patient. The generalized quantities provide performance characteristics that consider the complete imaging system, but reduce to a description of the detector properties without magnification or scatter. We have evaluated a new neurovascular angiography imaging system based on a region of interest (ROI) microangiographic detector using these generalized quantities. A uniform head-equivalent phantom was used as a filter and x-ray scatter source. This allowed the study of all properties of the detector under clinically relevant x-ray spectra and x-ray scatter conditions. Realistic focal spots (0.8 mm nominal), beam energies (60-100 kVp), and detector exposures (0.8-2.3 mR) were used, and the effects of different scatter fractions (0-0.62) resulting from changing the beam size (0-100 cm2) were investigated. The generalized MTF and DQE were found to have very little dependence on the tube voltage and the detector entrance exposure. Magnification, with the focal spot used, results in a large decrease of the generalized DQE at higher frequencies (about 100-fold at 10 cycles/mm), but a significantly smaller decrease at lower frequencies. Scatter on the other hand, causes a constant drop in the generalized DQE (factor of 3 for scatter fraction 0.3) for all frequencies. Our results show that there are tradeoffs in the choice of the different system parameters; therefore this methodology of studying the imaging system as a whole could provide guidance in system design.

A micro-angiographic detector was designed and its performance was previously tested to evaluate its feasibility as an improvement over current x-ray detectors for neuro-interventional imaging. The detector was shown to have a modulation transfer function value of about 2% at the Nyquist frequency of 10 cycles/mm and a zero frequency detective quantum efficiency [DQE(0)] value of about 55%. An assessment of the system was required to evaluate whether the current system was performing at its full potential and to determine if any of its components could be optimized to further improve the output. For the purpose, in this study, the parallel cascade theory was used to analyze the performance of the detector under neuro-angiographic conditions by studying the output at the various stages in the imaging chain. A simple model for the spread of light in the CsI(Tl) entrance phosphor was developed and the resolution degradation due to K-fluorescence absorption was calculated. The total gain of the system was found to result in 21 e(-) (rms) detected at the charge coupled device per absorbed x-ray photon. The gain and the spread of quanta in the imaging chain were used to calculate theoretically the DQE using the parallel cascade model. The results of the model-based calculations matched fairly well with the experimental data previously obtained. This model was then used to optimize the phosphor thickness for the detector. The results showed that the area under the DQE curve had a maximum value at 150 microm of CsI(Tl), though when weighted by the squared signal in frequency space of a 100-microm-diam iodinated vessel, the integral DQE reached a maximum at 250 microm of CsI(Tl). Further, possible locations for gain increase in the imaging chain were determined, and the output of the improved system was simulated. Thus a theoretical analysis for the micro-angiographic detector was performed to better assess its potential.

Use of cone-beam computed tomography (CBCT) is becoming more frequent. For proper reconstruction, the geometry of the CBCT systems must be known. While the system can be designed to reduce errors in the geometry, calibration measurements must still be performed and corrections applied. Investigators have proposed techniques using calibration objects for system calibration. In this study, the authors present methods to calibrate a rotary-stage CB micro-CT (CBμCT) system using only the images acquired of the object to be reconstructed, i.e., without the use of calibration objects. Projection images are acquired using a CBμCT system constructed in the authors' laboratories. Dark- and flat-field corrections are performed. Exposure variations are detected and quantified using analysis of image regions with an unobstructed view of the x-ray source. Translations that occur during the acquisition in the horizontal direction are detected, quantified, and corrected based on sinogram analysis. The axis of rotation is determined using registration of antiposed projection images. These techniques were evaluated using data obtained with calibration objects and phantoms. The physical geometric axis of rotation is determined and aligned with the rotational axis (assumed to be the center of the detector plane) used in the reconstruction process. The parameters describing this axis agree to within 0.1 mm and 0.3 deg with those determined using other techniques. Blurring due to residual calibration errors has a point-spread function in the reconstructed planes with a full-width-at-half-maximum of less than 125 μm in a tangential direction and essentially zero in the radial direction for the rotating object. The authors have used this approach on over 100 acquisitions over the past 2 years and have regularly obtained high-quality reconstructions, i.e., without artifacts and no detectable blurring of the reconstructed objects. This self-calibrating approach not only obviates calibration runs, but it also provides quality control data for each data set.

CAD has the potential to improve diagnostic accuracy in the detection of lung nodules on digital radiographs.

We present a new technique based on the method developed by Metz and Fencil for estimation of the 3D imaging geometry and 3D object configurations from biplane angiographic acquisitions. The new method employs the 3D configuration of points calculated by the Metz–Fencil technique as an initial estimate. A 3D Procrustes algorithm is employed to translate, rotate, and scale the configuration until it aligns optimally with the set of lines that connects a focal spot with the corresponding set of image points. This alignment procedure is applied independently for each view. The rotation and translation that relate the two aligned data sets are then determined by an additional 3D Procrustes calculation. These steps are applied iteratively. Evaluations were based on Monte Carlo simulation and phantom studies. With this new technique, the mean absolute errors in magnification, in the relative position of the points, and in the angles defining the rotation and translation matrices were approximately 3.0%, 1.5 mm, and 5° and 3°, respectively, for rms input errors in the image data up to 2.0 pixels (0.7 mm). Errors in the results can be as small as 0.5%, 0.16 mm, 0.6°, and 0.3°, respectively, if input image‐data error is 0.035 mm. The improvement of the Metz–Fencil technique described here may provide a basis for precise estimation of the biplane imaging geometry and the 3D positions of vessel bifurcation points.

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Minimally invasive interventions are rapidly replacing invasive surgical procedures for the most prevalent human disease conditions. X-ray image-guided interventions carried out using the insertion and navigation of catheters through the vasculature are increasing in number and sophistication. In this article, we offer our vision for the future of this dynamic field of endovascular image-guided interventions in the form of predictions about (1) improvements in high-resolution detectors for more accurate guidance, (2) the implementation of high-resolution region of interest computed tomography for evaluation and planning, (3) the implementation of dose tracking systems to control patient radiation risk, (4) the development of increasingly sophisticated interventional devices, (5) the use of quantitative treatment planning with patient-specific computer fluid dynamic simulations, and (6) the new expanding role of the medical physicist. We discuss how we envision our predictions will come to fruition and result in the universal goal of improved patient care.